The present invention relates to a bloom inhibitor. More precisely, the present invention relates to a bloom inhibitor comprising an alkylene oxide adduct of a saponified ethylene-saturated carboxylic acid vinyl ester copolymer and a polyether compound.
Surface deposition of vulcanization accelerator or the like contained in vulcanized rubbers, so-called phenomenon, occurs during storage of the vulcanized rubbers.
As a measure for inhibiting this phenomenon, a method in which polyethylene glycol is used as a bloom inhibitor has been proposed(JP-B-59-15345). When, however, vulcanized rubbers obtained according to this method were stored for a long period, the phenomenon could not be effectively prevented.
As a bloom inhibitor for resolving this problem, use of an alkylene oxide adduct of a saponified ethylene-saturated carboxylic acid vinyl ester copolymer (hereinafter, referred simply to as the adduct) has been proposed (Japanese Patent No. 2,564,991).
The present inventors have conducted an extensive research for finding a superior bloom inhibitor. As the result, they have found the fact that a bloom inhibitor in which the adduct is combined with a polyether compound exhibits a remarkably superior effect in prevention of the phenomenon and is capable of inhibiting the phenomenon of vulcanized rubbers for a long period. Thus, the present invention has been completed.
The present invention provides a bloom inhibitor which comprises an alkylene oxide adduct of a saponified ethylene-saturated carboxylic acid vinyl ester copolymer (hereinafter referred to as ingredient (A)), and a polyether compound (hereinafter referred to as ingredient (B)).
Examples of the ingredient (A) includes a product which is produced by copolymerizing ethylene and a saturated carboxylic acid vinyl ester, then completely or partially saponifying the obtained copolymer to give a saponification product and subsequently adding an alkylene oxide to said saponification product (JP-A-3-227307).
The method for copolymerizing the ethylene and saturated carboxylic acid vinyl ester is not particularly limited. A conventional method, such as the high-pressure radical polymerization, can be adopted. The saturated carboxylic acid vinyl ester as a raw material for copolymerization is not particularly limited. Preferred examples thereof include vinyl esters of an aliphatic carboxylic acid having about 2 to 4 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl butyrate and a mixture thereof. Amongst them, vinyl acetate is the most preferred. In addition to ethylene and the saturated carboxylic acid vinyl ester, a small amount of xcex1,xcex2-unsaturated carboxylic acid alkyl ester, such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate or a mixture of two or more of them, can be used as another raw material for copolymerization.
The content of ethylene in the ethylene-saturated carboxylic acid vinyl ester copolymer is usually about 1 to 90% by weight and preferably about 40 to 80% by weight. The number average molecular weight of the copolymer is usually about 1,000 to 20,000 and preferably about 1,000 to 10,000.
The method for saponification reaction of the ethylene-saturated carboxylic acid vinyl ester copolymer is again not particularly limited. For example, it may be conducted according to a general manner of a saponification with an alkali in the presence of an alcohol. In addition, other saponification methods such as methods of a heterogeneous liquid system using alcohol. alcoholic solvent system, a pellet dispersion system in alcohol and the like can suitably be adopted depending on characteristic properties varied by the molecular weight of, the content of the saturated carboxylic acid vinyl ester in, or else of the ethylene-saturated carboxylic acid vinyl ester copolymer.
The suitable rate of saponification depends on content of the saturated carboxylic acid vinyl ester in the ethylene-saturated carboxylic acid vinyl ester copolymer and is not particularly limited. Usually, it is about 30 to 100%, preferably about 50 to 100%.
The method for adding an alkylene oxide to the saponified ethylene-saturated carboxylic acid vinyl ester copolymer is not particularly limited. Generally, it is performed by reacting the alkylene oxide in the gaseous phase on said saponified copolymer.
Although the alkylene oxide is not particularly limited, it is preferably a compound having about 2 to 4 carbon atoms such as ethylene oxide, propylene oxide and butylene oxide. Amongst them particularly preferred is ethylene oxide. Two kinds of the alkylene oxide can be used. The addition may be the block addition or the random addition.
Although the amount of addition of the alkylene oxide is not particularly limited, it is usually about 20 to 1,000 parts by weight, preferably about 50 to 500 parts by weight, based on 100 parts by weight of the saponified copolymer.
Examples of the ingredient (B) in the invention include polyether compounds having an ether bond in its main chain. Specific examples include polyethylene glycol, polypropylene glycol, polytetramethylene glycol and polyphenylene ether. Amongst them, polyethylene glycol and polypropylene glycol are preferred and polyethylene glycol is particularly preferred.
The number average molecular weight of the ingredient (B) is usually within a range of about 1,000 to 20,000. The compounds within the range of about 2,000 to 10,000 are preferred. When the number average molecular weight is less than 1,000, the polyether compound is liable to deposit on the surface of rubber. When the number average molecular weight exceeds 20,000, the molecular motion of the polyether compound in the rubber composition is lowered. Therefore, the preventing effect against the phenomenon is liable to be decreased.
The weight ratio of the ingredient (A) and the ingredient (B) is usually about 35:65 to 65:35 and preferably about 40:60 to 60:40.
In addition to the ingredient (A) and the ingredient (B), the bloom inhibitor of the present invention may optionally contain one or more other ingredients such as inorganic filler. Examples of the inorganic filler include silica, talc, clay, calcium carbonate, aluminum hydroxide, aluminum oxide, titanium oxide and carbon black. As the inorganic filler, silica and calcium carbonate are particularly preferred.
The bloom inhibitor of the invention can be produced by mixing the ingredient (A) and the ingredient (B) together with, if necessary, another ingredient such as the inorganic filler.
The rubber composition of the invention comprises a rubber, the ingredient (A) and the ingredient (B). In addition, if necessary, it may further comprise a compounding additive, vulcanizing agent, vulcanization accelerator and the like.
The weight ratio of the ingredients in the rubber composition is usually about 0.1 to 10 parts by weight of the ingredient (A) and about 0.1 to 10 parts by weight of the ingredient (B), based on the 100 parts by weight of the rubber. Above all, about 0.2 to 1 parts by weight of the ingredient (A) and about 0.2 to 1 parts by weight of the ingredient (B) are preferred and, about 0.2 to 0.5 parts by weight of the ingredient (A) and about 0.2 to 0.5 parts by weight of the ingredient (B) are more preferred.
The weight ratio of the ingredient (A) and the ingredient (B) in the rubber composition is usually about 35:65 to 65:35 and preferably about 40:60 to 60:40.
When the weight ratio of the ingredient (A) exceeds 10 parts by weight based on 100 parts by weight of the rubber, the strength of the obtained vulcanized rubber is liable to be lowered. When the ingredient (A) is less than 0.1 part by weight, the preventing effect against the phenomenon of vulcanized rubber is liable to be insufficient.
When the ingredient (B) exceeds 10 parts by weight based on 100 parts by weight of the rubber, the ingredient (B) is liable to deposit from the obtained vulcanized rubber. When the ingredient (B) is less than 0.1 part by weight, the preventing effect against the phenomenon of vulcanized rubber is liable to be insufficient.
As the rubber, natural and synthetic rubbers can be used, with the synthetic rubbers being preferred.
Specific examples of the synthetic rubbers include ethylene-xcex1-olefin copolymer rubber, styrene-butadiene copolymer rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR) and isoprene-isobutylene copolymer rubber (IIR). Particularly preferred is the ethylene-xcex1-olefin copolymer rubber.
The ethylene-xcex1-olefin copolymer rubber includes, for example, copolymer rubbers constituting of ethylene and one or more xcex1-olefins (EPM) and copolymer rubbers constituting of ethylene, one or more xcex1-olef in and one or more unconjugated dienes (EPDM). Examples of the xcex1-olefin include propylene, 1-pentene and 1-hexene. Examples of the unconjugated diene include dicyclopentadiene, ethylidenenorbornene, 1,4-hexadiene, methyltetrahydroindene and methylnorbornene.
Examples of the compounding additive include fillers, stabilizers such as antioxidants and antiozonants, cross-linking agents, retarders, peptizers, processing aids, waxes, oils, stearic acid, tackifiers, methylene doners and methylene acceptor organic cobalt compounds.
Examples of the filler include inorganic fillers described above and other fillers such as coumarone-indene resins, high-styrene resins and phenol resins. Amongst them, inorganic fillers are preferred and silica, talc, calcium carbonate and carbon black are particularly preferred.
Examples of the vulcanization agent include sulfur compounds and organic peroxides. Examples of the sulfur compounds include sulfur, sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, tetramethylthiuram disulfide and selenium dimethyldithiocarbamate. Amongst them, sulfur is preferred.
Examples of the organic peroxides as the vulcanization agent include dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, di-tert-butylperoxide, di-tert-butylperoxy-3,3,5-trimethylcyclohexane and tert-butylhydroperoxide. Amongst them, dicumyl peroxide, tert-butylperoxide, di-tert-butylperoxide and di-tertbutylperoxy-3,3,5-trimethylcyclohexane are preferred.
When an organic peroxide is used as the vulcanization agent, co-use with a vulcanization aid is preferred. Examples of the vulcanization aid include sulfur, quinone dioxime compounds such as p-quinone dioxime, methacrylate compounds such as polyethyleneglycol dimethacrylate, allyl compounds such as diallyl phthalate and triallyl cyanurate, maleimide compounds such as bismaleimide and divinylbenzene.
When a sulfur compound is used as the vulcanization agent, co-use with a vulcanization accelerator is preferred. Examples of the vulcanization accelerator include thiazol compounds such as N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, N,N-diisopropyl-2-benzothiazole sulfenamide, 2-mercaptobenzothiazole, 2-(2,4-dinitrophenyl)mercaptobenzothiazole, 2-(2,6-diethyl-4-morpholinothio)benzothiazole and dibenzothiazole-benzothiazyl disulfide, guanidine compounds such as diphenyl guanidine, triphenyl guanidine, di-o-tolylguanidine, o-tolylbiguanide and diphenylguanidine phthalate, aldehyde-amines or aldehyde-ammonia compounds such as acetaldehyde-aniline condensate, hexamethylenetetramine and acetaldehyde-ammonia, immidazoline compounds such as 2-mercaptoimmidazoline, thiourea compounds such as thiocarbanilide, diethylthiourea, dibutylthiourea, trimethylthiourea and di-o-tolylthiourea, thiuram compounds such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide and dipentamethylenethiuram tetrasulfide, dithio-salt compounds such as zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc di-n-butyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, selenium dimethyldithiocarbamate and tellurium diethyldithiocarbamate, xanthate compounds such as zinc dibutylxanthate, and zinc oxide.
The rubber composition of the present invention can be obtained, for example, by charging the ingredient (A), the ingredient (B) and, if necessary, any compounding additives in a closed kneader, an oven rolls, an extruder or the like, followed by kneading them. Then, the obtained kneaded product is combined, if necessary, with a vulcanization agent, vulcanization accelerator and the like to give a rubber composition of the present invention.
As the ingredient (A), the ingredient (B) and any compounding additives used if necessary, a premixed compound can be used.
A vulcanized rubber in which blooming is prevented can be obtained by vulcanizing the rubber composition obtained in the above manner, which contains a vulcanization agent and others.